Add onChanged events to the extension settings API, both from sync and between

chrome/browser/extensions/syncable_extension_settings_storage.h

Index: chrome/browser/extensions/syncable_extension_settings_storage.h
diff --git a/chrome/browser/extensions/syncable_extension_settings_storage.h b/chrome/browser/extensions/syncable_extension_settings_storage.h
index 39f4607001efe39c275d36f9630e5b64bc7277dc..32b2d739ebff46cfa81a2451d7379f3817291e87 100644
--- a/chrome/browser/extensions/syncable_extension_settings_storage.h
+++ b/chrome/browser/extensions/syncable_extension_settings_storage.h
@@ -8,7 +8,9 @@
 
 #include "base/compiler_specific.h"
 #include "base/memory/weak_ptr.h"
+#include "base/observer_list_threadsafe.h"
 #include "base/values.h"
+#include "chrome/browser/extensions/extension_settings_observer.h"
 #include "chrome/browser/extensions/extension_settings_storage.h"
 #include "chrome/browser/extensions/extension_setting_sync_data.h"
 #include "chrome/browser/sync/api/syncable_service.h"
@@ -18,7 +20,9 @@
 class SyncableExtensionSettingsStorage : public ExtensionSettingsStorage {
  public:
   explicit SyncableExtensionSettingsStorage(
-      std::string extension_id,
+      const scoped_refptr<ObserverListThreadSafe<ExtensionSettingsObserver> >&
+          observers,
+      const std::string& extension_id,
       // Ownership taken.
       ExtensionSettingsStorage* delegate);
 
@@ -62,6 +66,9 @@ class SyncableExtensionSettingsStorage : public ExtensionSettingsStorage {
   SyncError OverwriteLocalSettingsWithSync(
       const DictionaryValue& sync_state, const DictionaryValue& settings);
 
+  // List of observers to settings changes.
+  scoped_refptr<ObserverListThreadSafe<ExtensionSettingsObserver> > observers_;
+
   // Id of the extension these settings are for.
   std::string const extension_id_;